The present invention relates to a material for bits and more particularly to a material for bits such as used for drilling igneous rock in a high temperature geothermal formation.
Since bits such as used for drilling a geothermal well and the like must be able to resist wear, impact and temperature, hitherto carburizing steel, such as classified under the appellations SAE 4815, 8720, 4620 and 9310, etc. has been widely used after subjection to a carburizing treatment. However, these carburizing steels have such defects as that they do not exhibit sufficient resistivity to wear such as caused by heavy contact with rocks during the drilling, penetration of debris from the rocks being excavated into the bearing means of the bit, etc., and their resistivity to wear remarkably deteriorates at an elevated temperature of 150.degree. C. or thereabouts since they easily soften at that temperature. Further, in an insert type bit, when it is used for a heavy drilling operation accompanying a temperature rise, or in a well in an environment where the temperature in the well is 200.degree. C. or more, as in a geothermal well, since the cutter blade of the bit of this type which is made of hard metal is subjected to strong impacts, a twisting action, a bending action, etc. during the drilling, not only do slackening and bending of the cutter blade occur, but also in extreme cases, the cutter blade may fall out, and soon, so that the life of the bit shortened.